This disclosure relates to test and measurement instruments and related devices, and in particular, to a distributed time-interleaved acquisition digital down-conversion method and system.
Traditionally, test and measurement instruments such as spectrum analyzers and vector analyzers have had minimal triggering capabilities and/or limited real-time bandwidth. Mixed-Domain Oscilloscopes (MDOs) represent a new product category of test and measurement devices, which integrate many of the spectral acquisition, triggering, and display capabilities of Real-Time Spectrum Analyzer (RTSA) products with the functionality of traditional oscilloscope products, in addition to supporting a wide range of acquisition span bandwidths, up to very wide real-time bandwidths supported by time-interleaved acquisition systems. In addition to supporting time domain features of traditional oscilloscopes and frequency domain features of RTSAs, the MDO products enable cross-correlation between both domains for acquisition, triggering, display, and analysis functions.
In such newer types of products, the RF input signal is digitally down-converted to produce I (in-phase) and Q (quadrature) baseband component information from the RF signal. More specifically, the RF signal is numerically multiplied with a sine and cosine, thereby generating the I and Q component information, which contains all of the information present in the original RF signal (within the span of interest). The acquisition data can then be further decimated if the desired span of interest is less than the maximum bandwidth in the system. Thus, this allows a longer period of time to be acquired into acquisition memory for cases where there are narrower spans of interest, given the constraint of a fixed acquisition memory size. Supporting a longer acquisition time span, in turn, allows a narrower resolution bandwidth for spectral analysis modes.
In conventional oscilloscopes and digitizers, time-interleaved acquisition is an approach for building test and measurement device acquisition systems with scalable sample rate and bandwidth and to extend acquisition systems beyond the capabilities of individual analog to digital converter (ADC) and/or digitizer components. For example, FIG. 1 shows a conventional example of a time-interleaved acquisition system used in oscilloscopes. A high-bandwidth sampler such as a track and hold component 105 is used to distribute sampled versions of the input signal 130 to multiple ADCs 110 with appropriate offsets in sampling time, based on the aggregate sample rate of the acquisition system and the total number of interleaved ADC and/or digitizer components.
A digitizer component such as component 115 is then used to process the incoming samples and store them in acquisition memory 120. The digitizer component 115 is a type of building block for acquisition, triggering, display, and analysis in an oscilloscope device. There is usually some form of interconnect between the different digitizer components for combining the time-interleaved acquisition data samples for further processing and analysis, which results in a coherent waveform 125 at the full sample rate of the acquisition system.
Prior approaches to supporting mixed-domain functionality primarily target single-digitizer component systems, which limits the sample rate and real-time bandwidth that can be acquired. To support a greater frequency range in an RF acquisition system traditionally has required expensive RF oscillator and mixer components to down-convert the input signal in the analog domain prior to the ADC component. This type of system is still limited to the bandwidth of a single ADC, in terms of the bandwidth span that can be acquired in real-time.
It would be desirable to have an acquisition technique that distributes digital down-conversion (DDC) functionality among multiple distributed time-interleaved acquisition components. It would also be desirable to support acquisitions over longer time spans, thereby enabling a lower spectral resolution bandwidth. In addition, it would be desirable to efficiently acquire spectral data from a narrower frequency band of interest anywhere within the aggregate bandwidth of the time-interleaved system and to support the reconstruction of acquired down-converted waveform data from the time-interleaved digitizer components stored in memory associated with each distributed acquisition component.